Heat exchangers having folded flat tubes are well known in the art. Such heat exchangers typically include a plurality of the folded flat tubes spaced apart and arranged in parallel and extending between an inlet header tank and an outlet header tank. The inlet header tank receives a first fluid and distributes the first fluid between a plurality of flow pathways formed within the flat tubes. The first fluid exchanges heat energy with a second fluid flowing through the spaces between adjacent ones of the flat tubes. After exchanging the heat energy within the flat tubes, the first fluid is recombined within the outlet header tank before exiting the heat exchanger.
One common construction of a flat tube includes folding a sheet of aluminum into a tubular structure wherein two opposing edges of the sheet are brought together and then brazed or welded at the resulting seam to form a substantially B-shaped flat tube. The central seam of the B-shaped flat tube is typically further reinforced by adding at least one fold to the opposing edges of the sheet. The folded over portions of the sheet of aluminum are positioned to abut an inner surface of the flat tube along a length thereof to form a longitudinally extending partition, wherein the partition divides a hollow interior of each of the flat tubes into two flow separate paths while also structurally reinforcing the flat tube along the central seam of the tube. This type of flat tube construction is disclosed in U.S. Pat. No. 5,579,837 to Yu et al., which is hereby incorporated by reference in its entirety.
One potential issue faced by the traditional B-shaped flat tube construction occurs as a result of the effects of thermal cycling. The repeated presence of varying characteristics within different portions of each of the tubes, such as varying temperatures experienced in different regions of each of the tubes, may lead to the formation of a bending moment within each of the tubes, such as between two adjacent flow channels formed within each of the tubes. The formation of such bending moments may affect the durability of such tubes when exposed to extended periods of thermal cycling including varying temperatures experienced between the two flow channels of each of the tubes.
The B-shaped folded flat tube construction has been found to be particularly susceptible to thermal cycling failure at an intersection of each of the tubes and each of the header tanks. Each of the tubes is inserted into an opening formed in each of the header tanks, the opening having a cross-sectional shape substantially similar to that of an outer surface of each of the tubes, thereby restricting outward deformation of the outer surface of each of the tubes. Concurrently, the central partition adds rigidity to the interior of each of the tubes further restricting relative movement between the opposing surfaces of each of the tubes adjacent the central partition. The added rigidity adjacent the intersection of each of the tube ends and each of the header tanks exacerbates the incidence of failure due to thermal cycling because the different portions of the tubes experiencing different degrees of thermal expansion are restricted from moving and deforming relative to each other during use of the heat exchanger. The restricted motion may in some circumstances lead to elevated stresses within portions of each of the tubes that can lead to permanent deformation or eventual failure adjacent each of the header tanks.
It would therefore be desirable to produce a tube for use in a heat exchanger having multiple flow channels while also preventing the incidence of failure at an intersection of the tube and an opening in a header tank configured to receive an end of the tube.